Chapter 19: Disorders of Visual Function

The study of visual function disorders encompasses abnormalities affecting the accessory structures, the globe itself, and the neural pathways leading to the cerebral cortex. Key conditions of the anterior eye include eyelid anomalies like ptosis, entropion, and ectropion, alongside inflammation such as blepharitis, hordeolum, and chalazion. The lacrimal system is often involved in dry eye syndrome, categorized as aqueous-deficient or evaporative, and dacryocystitis. Inflammation of the conjunctiva, known as pink eye, must be clearly distinguished from more critical anterior segment diseases like infectious keratitis—which involves the cornea and may be caused by Herpes Simplex or Acanthamoeba—or acute angle-closure glaucoma. Glaucoma is critically defined as an optic neuropathy, primarily characterized by damage to optic nerve axons resulting from elevated intraocular pressure (IOP). IOP is maintained by the balance of aqueous humor secretion and outflow through the trabecular meshwork and the canal of Schlemm; obstruction leads to either the chronic, often asymptomatic Primary Open-Angle Glaucoma or the acutely painful Angle-Closure Glaucoma. Moving posteriorly, common lens disorders include refractive errors like myopia (nearsightedness) and hyperopia (farsightedness), the age-related loss of accommodation termed presbyopia, and cataracts, which are lens opacities—most commonly senile—that scatter light and require surgical replacement. Retinal pathologies, typically painless, include retinopathies, most notably proliferative diabetic retinopathy characterized by fragile neovascularization; age-related macular degeneration (AMD), which causes central vision loss in dry (atrophic) and wet (exudative) forms; and retinal detachment, where the neurosensory retina separates from its nourishing pigment layer, often rhegmatogenous in origin. Furthermore, the malignant childhood tumor retinoblastoma is frequently identified by the white pupil reflex (leukocoria). Finally, neural pathway deficits caused by lesions along the optic nerve, chiasm, or tract lead to characteristic visual field losses such as hemianopia or quadrantanopia. Misalignment of the extraocular muscles, called strabismus (squint), frequently results in amblyopia (lazy eye), a critical developmental decrease in visual acuity requiring early intervention during visual immaturity.